For controlling the climate of aircraft cabins hot air is normally taken from the engines of an aircraft. This hot air, which is called bleed air, passes through an air line including a flow control valve for controlling the flow volume to an air conditioning unit wherein the hot air is cooled to the temperature required in the aircraft cabin. In aircrafts in the cabins of which different climate zones are to be set it is also known to cool down the hot air intake by means of the air conditioning unit to the lowest temperature requirement of the various climate zones and, in order to be able to provide air for climate zones with higher temperature requirements, to guide away a certain portion of the hot air upstream from the air conditioning unit and to mix it with the air cooled by the air conditioning unit in accordance with the respective temperature requirement. With such a system, known also as the “Trim Air System”, the required temperature in the individual climate zones of an aircraft cabin can be adjusted individually. If the aircraft cabin to be air-conditioned is very large, such systems are provided in multiples, e.g. double, i.e. two or more air conditioning units are provided, each comprising its own hot air supply and flow control.
There is a problem with the aforementioned systems in that in the event of a failure of all available air conditioning units the flow control throttles the volume of the hot air intake to the air conditioning units to zero in order to prevent the air conditioning unit from being damaged by the hot air. In such an event pressurization and temperature control of the aircraft cabin are no longer possible (it is to be noted in this context, that the term “aircraft cabin” as used herein includes the cockpit of an aircraft). In order to supply the aircraft occupants with the necessary fresh air in the event of a failure of all available air conditioning units it is known according to the state of the art to open a flap in the aircraft fuselage and to thereby allow ambient air to enter the aircraft. However at the normal flight altitudes of an aircraft and in cold regions even in a low-flying aircraft, the ambient temperature can be below −50° C. or even −60° C. with the result that the temperature in the aircraft cabin can fall to values below 18° C. due to the intake of cold outside air. Such low internal temperatures, however, are impermissible for either the passengers of an aircraft or its crew without additional protection.
Starting from the prior art system as described at the outset the object of the invention is to provide remedy and to propose a system that permits temperature control of the aircraft cabin even in the event of failure of all available air conditioning units.